1. Field of the Invention
The present invention relates to a photoreceptor, an image formation method, an image forming apparatus, and process cartridge.
2. Discussion of the Background
Recently, organic photoconductors (photoreceptors) have been used in place of inorganic photoreceptors for a photocopier, a facsimile machine, a laser printer and a multifunctional device thereof in light of performances and advantages. Specific reasons for this replacement are, for example, (1) good optical characteristics, for example, width of the range of optical absorption wavelength and size of the amount of absorption of light; (2) electric characteristics, for example, high sensitivity and stable chargeability; (3) a wide selection of materials; (4) ease of manufacturing; (5) inexpensive cost; and (6) toxic-free property.
In addition, the trend of the size reduction of an image forming apparatus has accelerated the size reduction of an image bearing member (photoreceptor). Therefore, with the advancement of high speed performance and maintenance-free, an image bearing member having high durability has been desired. From this point of view, an organic photoconductor is soft in general and easy to wear down because the surface layer thereof is mainly made of a low molecular weight charge transport material and an inert polymer. Thus, an organic photoconductor repetitively used in the electrophotography process tends to be abraded under mechanical stress by a developing system or a cleaning system. Such abrasion of a photoreceptor causes deterioration of electric characteristics, for example, the sensitivity and the chargeability, resulting in production of abnormal images having, for example, low image density and background fouling. Local abrasion damage to a photoreceptor causes streaks on an image due to bad cleaning performance on the photoreceptor.
However, an organic photoconductor (photoreceptor) having a hardened surface or a protective layer containing a filler has been used in recent years, which has drastically improved the anti-abrasion property and anti-damage property of the organic photoconductor.
However, a photoreceptor having an improved anti-abrasion property is vulnerable to a problem such as vibration and turning inward or outward of a cleaning blade in the cleaning process.
The circumference surface of a photoreceptor is cleaned in the cleaning process among the electrophotography processes in which residual toner remaining on the photoreceptor after the transfer process is removed to obtain vivid and clear images.
In a cleaning method taking such a system, the residual toner remaining on the photoreceptor after transfer is scraped by a cleaning blade, which is provided to fill the gap between the photoreceptor and the cleaning blade by making the cleaning blade in contact with the photoreceptor to prevent the toner from slipping through the gap. This cleaning method is dominant in terms of cost, ease of designing, etc.
The vibration of a cleaning blade is a phenomenon in which the cleaning blade vibrates due to an increase of the friction between the cleaning blade and the surface of the photoreceptor. Turning inward or outward of a cleaning blade is a phenomenon in which the cleaning blade turns over along the moving direction of the photoreceptor.
Currently, increasing the contact pressure between the cleaning blade and the photoreceptor and the rubber hardness of the cleaning blade is inevitable to deal with size reduced toner demanded for production of quality images. Thus, the problems of vibration and turning inward or outward of a cleaning blade are highlighted.
A known method of reducing the vibration and turning inward or outward of the cleaning blade is to reduce the friction resistance between the cleaning blade and the photoreceptor by suitably roughening the surface of a photoreceptor to decrease the contact area between the cleaning blade and the surface of the photoreceptor.
Unexamined published Japanese patent application No. (hereinafter referred to as JOP) S52-026226 describes a technology of roughening the surface of a photoreceptor by containing particles in the surface layer.
In addition, JOP H02-139566 describes another technology of grinding the surface layer of a photoreceptor with polishing material having a film form to roughen the surface.
These technologies are effective to solve the vibration and turning inward or outward problem of a cleaning blade mentioned above but face a new problem that toner easily slips through the cleaning blade because the surface of the photoreceptor is roughened.
Slipping through of toner is a phenomenon in which toner slips through between the cleaning blade and the photoreceptor. JOP 2005-99688 describes a technology in which filler particulates are dispersed in the surface layer of the photosensitive layer of a photoreceptor and the surface layer is a cross linked resin layer formed by curing a radical polymerizable monomer having three or more functional groups without a charge transport structure, and a radical polymerizable monomer having a charge transport structure.
However, the contact area between the cleaning blade and the photoreceptor is large in this technology, which involves the problem of the vibration and/or turning inward or outward of the cleaning blade.
In addition, JOP 2006-11047 describes a technology in which a myriad of linear scars crossing each other are evenly formed on the surface of the photoreceptor.
Although the vibration and turning inward or outward of the cleaning blade can be prevented, toner tends to slip through, which causes bad cleaning performance. As described above, having a good combination of prevention measures against vibration or turning inward or outward of a cleaning blade and slipping through of toner is difficult.